1. Field of the Invention
The present invention relates to a light transmitting hard coat film for use in touch panels, in particular, to a light transmitting hard coat film for use in touch panels which has a high light transmittance and can produce transmitted light of blue color.
2. Description of the Related Art
Touch panels have been used for various applications such as ATMs installed in banks, ticket machines and information terminals in railroad stations, boarding procedure terminals in airports and electronic organizers. Touching the surface of the touch panels with a finger or a pen, etc. makes it possible for the touched input position to be recorded by the above machines or terminals, etc.
A typical analog type of touch panels have a structure in which a first transparent conductive film is laminated on the surface of a glass board, a microdot spacer is formed on the surface of the first transparent conductive film, a second transparent conductive film is laminated on the first transparent conductive film with a space left between the first and the second transparent conductive films; and a transparent film is laminated on the second transparent conductive film. Touching the surface of the transparent film with a finger or a pen, etc. allows the portions of the two transparent conductive films for which no spacer is provided to come in contact with each other, which makes it possible for the touched input position to be recorded by the machine, terminal, or the like in which the touch panel is used.
This analog type of touch panels can usually be produced by laminating a glass board, on which a first transparent conductive film with microdot spacers formed on its surface is laminated, and a transparent film, on which a second transparent conductive film is laminated, with both the transparent conductive films facing each other and a space left between the both films.
Conventional transparent films on which transparent conductive films are laminated include, for example, a laminate of an indium-tin oxide film (ITO film) and a polyethylene terephthalate film (PET film).
However, in the laminate of an ITO film and a PET film for use in touch panels, its total light transmittance is low compared with a clear hard coat PET film and the color of its transmitted light is yellow, which gives rise to a problem that the produced touch panels is insufficient in visibility, operatability and high-quality impression.
In International Patent Publication WO 00/63924, a transparent touch panel is described, which is a laminate of: a transparent substrate such as a glass board, a polycarbonate sheet or a polyethylene terephthalate sheet; a hard coat layer composed of acrylic resin, etc.; a high refractive index layer composed of ZrO2, TiO2, Al2O3, etc. whose refractive index is 1.50 to 2.50; a low refractive index layer composed of SiO2, MgF2, etc. whose refractive index is 1.35 to 1.60; and a transparent conductive layer. In this transparent touch panel, its visibility and operatability have been improved to some extent, but they are still insufficient; and moreover, it has a problem of producing transmitted light of yellow color.
In Japanese Patent Laid-Open No. 2000-301648, a transparent touch panel is described which is a laminate of: a transparent substrate such as a polyethylene terephthalate film, a polycarbonate film or a polyarylate film; a hard coat layer composed of acrylic resin etc.; a high refractive index layer composed of a cross-linked product of alkoxides of titanium and zirconium whose refractive index is 1.7 to a refractive index larger than that of a transparent conductive layer by about 0.3; a low refractive index layer composed of a cross-linked product of silicon alkoxode, etc. whose refractive index is 1.35 to 1.5; and a transparent conductive layer.
In this touch panel, however, its transmitted light is colorless or slightly yellowish, but not blue, which is a color desired for touch panels to produce.
Thus, there have been demands for a hard coat film for use in touch panels which has a high total light transmittance and can produce transmitted light of blue color.